Conventionally, in a plant and a factory, a DCS (Distributed Control System) is established in order to implement an advanced automatic operation. In the distributed control system, field devices (a measurement device and a manipulation device) and a controller controlling the field devices are connected to each other through a network. Although most of the field device included in the distributed control system performs wire communications, recently there is a device (wireless field device) which performs wireless communications in conformity with an industrial wireless communication protocol such as ISA100.11a, WirelessHART (registered trademark), and so on.
An input/output part, a wireless communicator, and a control part are included in a housing of the wireless field device, and each part is operated by electric power supplied from a single power source. An input/output part performs measurement or operation of state quantity (for example, pressure, temperature, flow quantity, and so on) in an industrial process. The wireless communicator performs wireless communications in conformity with the industrial wireless communication protocol described above. The control part totally controls an operation of the wireless field device. Here, it is not necessary to connect the wireless field device to a communication line or a communication bus, different from the conventional field device. Since the wireless field device is basically installed in the plant independently, most of the wireless field device contains a battery as the single power source.
The following patent document 1 discloses that a wireless device is attached to the conventional field device which does not have a wireless communicator, and the wireless device is capable of operating the conventional field device as a wireless field device. Specifically, the wireless device disclosed in the following patent document 1 includes an interface, a wireless communicator, and a power source. The interface is connected to the conventional field device. The wireless communicator performs wireless communications. The power source supplies electric power to the conventional field device through the interface. In a case that a signal from the field device is input to the wireless device through the interface, the wireless device transmits the signal from the wireless communicator to a transmission destination (for example, a host controller). In a case that the wireless communicator receives a signal of which destination is the field device, the wireless device outputs the received signal to the field device through the interface.